Double parton distributions out of bounds in colour space

Abstract

We investigate the positivity of double parton distributions with a non-trivial dependence on the parton colour. It turns out that positivity is not preserved by leading-order evolution from lower to higher scales, in contrast to the case in which parton colour is summed over. We also study the positivity properties of the distributions at small distance between the two partons, where they can be computed in terms of perturbative splitting kernels and ordinary parton densities.

Colour evolution and infrared physics

“…The main purpose of this analysis and outlook is, however, to show that we can touch ground with first-principle definitions, an avenue which we will explore further. Beyond this observation we note that correlations among hadrons with certain momentum balances might actually be able to probe whatever (colour) interference the hard process allows to, since this will be imprinted in the evolution much in the same way as it has been observed in the case of double parton distributions for those processes where colour interference will mix these objects [40]. In fact, the general formula we envisage should be easily able to accommodate processes with incoming hadrons.…”

Color Reconnection Effects in $J/ψ$ Hadroproduction

“…It is important to stress, that the concept of the MPI in Monte Carlo event generators is quite different than for e.g. the hard double parton scattering, where for sufficiently inclusive observables the QCD factorization holds (see[47][48][49][50][51][52] and an overview in[53]). The soft MPI modeled in event generators are nonperturbative phenomena, thus existence of rather strong color correlations between different subsystems is a natural expectation.…”